The present invention is based on Japanese Patent Application No. 2000-174483, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a hydrogen storage and release apparatus using relatively low temperature heat gas generated from a micro gas turbine or the like in which storage and release of hydrogen can be performed efficiently.
2. Description of the Related Art
Recently, attention has been paid to a micro gas turbine electric power plant as a distributed electric source capable of generating electric power efficiently and capable of reducing the system size. The plant uses natural gas or biogas as fuel and the fuel is burned to operate a small-sized gas turbine to thereby generate electric power. However, the energy efficiency in the plant is not sufficiently high. A large amount of energy is lost as waste heat into exhaust gas. Therefore, a method for efficient use of the waste heat has been researched and a system of obtaining hot water from such waste heat has been proposed. However, the range of use of hot water or the like is limited and the whole amount of the hot water cannot be always used. Therefore efficient use of the waste heat is not sufficient and energy efficiency carried out by the whole plant has not been yet improved sufficiently.
Although the field of the application is different from the field of micro gas turbine, the Applicant of the present application has developed systems in which high-temperature waste heat or the like generated from a factory or the like is used as a driving source, and hydrogen storage alloys in combination with coolants are used for storing or releasing hydrogen to thereby make it possible to perform storage of hydrogen, purification of hydrogen, air-conditioning, refrigeration, heat migration, etc. When, for example, this system is applied to an air-conditioner, a high-temperature-side hydrogen storage alloy and a low-temperature-side hydrogen storage alloy are provided so that hydrogen can move between the two alloys. Further, high-temperature and high-pressure steam is obtained from waste heat and used as a heat medium to heat the high-temperature-side hydrogen storage alloy. The hydrogen storage alloy releases stored hydrogen when it is heated and then the released hydrogen is stored into the low-temperature-side hydrogen storage alloy. After that, when the high-temperature-side hydrogen storage alloy is cooled so as to generate hydrogen suction force, hydrogen is released from the low-temperature-side hydrogen storage alloy and stored into the high-temperature-side hydrogen storage alloy. On this occasion, cold heat is generated in the low-temperature-side hydrogen storage alloy. Hence, the cold heat is used as a heat source for air-conditioning. In this method, improvement in energy-utilizing efficiency can be attained because an air-conditioning output can be obtained by use of waste heat. Hence, if such air-conditioning or the like can be performed by the aforementioned system by use of waste heat discharged from the aforementioned micro gas turbine, total energy efficiency is improved greatly.
However, since this system uses exhaust gas discharged from a micro gas turbine in which the exhaust gas temperature is low, high-temperature and high-pressure steam cannot be obtained from the exhaust gas when the gas temperature is not sufficiently high. When the temperature of the steam is low, the hydrogen storage alloy cannot be heated sufficiently. As a result, hydrogen cannot be released securely. Hence, such the system cannot be operated well.
The present invention is made by taking the aforementioned circumstances into consideration and has an object to provide a hydrogen storage and release apparatus in which thermal energy is obtained efficiently from a relatively low temperature heat gas so that the thermal energy can be used as a driving source to make hydrogen stored and released by means of a hydrogen storage alloy.
That is, in order to solve the above problem, according to a first aspect of the present invention, there is provided a hydrogen storage and release apparatus comprising: a heat exchanging portion including hydrogen storage alloy containers each containing a hydrogen storage alloy for storing and releasing hydrogen; a heat exchanger body in which the heat exchanging portion is received, and into which a heat gas or coolant is introduced to perform heat exchange with the heat exchanging portion, and from which the heat gas or coolant is discharged after heat exchange; and a hydrogen-travelling passage connected to the hydrogen storage alloy containers so that hydrogen can move to the hydrogen storage alloy containers, the heat exchanging portion being set in such a manner that the heat exchanging efficiency on the heat gas discharge side of the heat exchanging portion is made higher continuously or stepwise than that on the heat gas introduction side of the heat exchanging portion.
According to a second aspect of the present invention, in the hydrogen storage and release apparatus as defined in the first aspect, preferably, the heat exchanging efficiency of the heat exchanging portion is adjusted by fins provided on a part or on the whole of an outer surface of the hydrogen storage alloy containers.
According to a third aspect of the present invention, in the hydrogen storage and release apparatus as defined in the first or second aspect, preferably, the hydrogen storage alloy containers are constituted by numbers of pipe bodies each containing a hydrogen storage alloy in its inside so as to be aerated, the numbers of pipe bodies being arranged in parallel so that gaps are formed among the pipe bodies, the heat exchanging portion being configured so that the heat gas passes through the gaps along a direction crossing a longitudinal direction of the pipe bodies.
According to a forth aspect of the present invention, in the hydrogen storage and release apparatus as defined in any one of the first through third aspects, preferably, the heat gas is a exhaust gas generated by combustion of fuel in a micro gas turbine.
According to the present invention, heat gas is used as a driving source. Exhaust gas of a micro gas turbine is a typical example of a source generating such heat gas. However, the source generating such heat gas according to the present invention is not limited thereto. The present invention may be applied to various kinds of generating sources. The present invention is originally based on the assumption that it is difficult to obtain high-temperature and high-pressure steam from the heat gas and the heat gas the temperature of which is relatively low is used. The temperature of the heat gas is not limited specifically to the relatively low one and higher-temperature heat gas may be also used. That is, the present invention provides a hydrogen storage and release apparatus which can be driven even by relatively low temperature heat gas, but the condition that the temperature of the heat gas is low is not the requirement of the present invention.
In the present invention, a hydrogen storage alloy is required for storing and releasing hydrogen. The hydrogen storage alloy is not limited to a specific kind of alloy and any suitable alloy maybe selected as the hydrogen storage alloy. Incidentally, in a system in which the hydrogen storage and release apparatus according to the present invention is disposed on the high temperature side and used in pair with a hydrogen storage and release apparatus disposed on the low temperature side, it is preferable to consider the heating temperature on the high temperature side and the temperature to be used on the low temperature side when hydrogen storage alloys are selected on the high and low temperature sides respectively.
These hydrogen storage alloys are contained in alloy containers in a condition that hydrogen can be stored and released. The storage and release of hydrogen can be achieved when an aeration material is disposed in each container or an aeration passage is secured to make it possible to move hydrogen. Each of the alloy containers is made of a material having a shape adapted for heat exchange or good in heat conduction because the alloy container serves as a heat exchanging portion. Consideration is made so that the contact between the alloy containers and the heat gas or the cooling heat medium (hereinafter referred to as xe2x80x9ccoolantxe2x80x9d) can be made effectively. Particularly, the contact and heat exchange between the alloy containers and the heat gas are important to the present invention.
As an example of the configuration in which such contact and heat exchange are performed well, there is provided a system in which: each of the hydrogen storage alloy containers is shaped like a pipe body containing a hydrogen storage alloy; the hydrogen storage alloy containers are arranged side by side vertically and horizontally as a large number of containers so that gaps are formed among the pipe bodies; and the heat gas passes through the gaps in a direction crossing the longitudinal direction of the pipe bodies. According to the aforementioned configuration, heat gas smoothly passes through the gaps among the pipe bodies. Hence, applying load to a generating source of the heat gas such as a micro gas turbine can be avoided. Moreover, the heat gas can be subjected to heat exchange with the pipe bodies efficiently because the heat gas flows along the outer walls of the pipe bodies. On this occasion, the heat gas flows in a direction crossing the longitudinal direction of the pipe bodies. Hence, variation in heat exchange efficiency can be reduced in the longitudinal direction of the pipe bodies, so that the hydrogen storage alloy contained in the pipe bodies can be heated evenly. Incidentally, the number of the pipe bodies to be arranged side by side vertically and horizontally, the size of the gaps, etc., may be determined suitably.
In the present invention, the heat exchanging portion is configured in such a manner that the heat exchanging efficiency on the heat gas discharge side becomes continuously or stepwise higher than that on the heat gas introduction side. Incidentally, the heat exchanging efficiency is determined on the basis of the magnitude of the quantity of heat transmitted to the hydrogen storage alloy containers by heat gas when amount and temperature of the heat gas are constant. It is to be assumed that the larger the quantity of heat is transmitted, the higher the heat exchanging efficiency is.
The setting of the heat exchanging efficiency can be performed by fins provided partly or on the whole of the outer surface of the hydrogen storage alloy containers. Specifically, fins may be provided selectively on hydrogen storage alloy containers located on the gas discharge side, or the surface area of fins, the number of the arranged fins and the density of arrangement of the fins may be changed in accordance with the position between the heat gas introduction side and the heat gas discharge side to thereby achieve the aforementioned configuration (when the efficiency is to be made high, the surface area of fins on the discharge side is increased, the number of fins disposed on the discharge side is increased or the density of arrangement of fins on the discharge side is increased.)
When the heat exchanging portion is constituted by a plurality of alloy containers each shaped like a pipe body as described above, the density of arrangement of such pipe bodies on the discharge side may be increased, the diameter of the pipe bodies on the discharge side may be increased or alloy containers of a good heat-conductive material different from alloy containers on the introduction side may be disposed on the discharge side so that the heat exchanging efficiency can be adjusted.
It is preferable that the adjustment of the heat exchanging efficiency is performed also upon the movement of the coolant in the same manner as described above. However, because cooling is performed rapidly, there is no large problem in uniformity in comparison with the case for heating. Also in the present invention, the aforementioned setting may be performed only upon the movement of heat gas.
The heat exchanging portion is located in the heat exchanger body into which a heat gas or coolant is introduced and from which the heat gas or coolant is discharged after heat exchange, so that heat exchange is performed between the heat exchanging portion and the heat gas or coolant. Any material may be used as the heat exchanger body so long as a gas flow path can be secured and heat exchange can be made between the heat exchanging portion and the heat gas or coolant. The methods for introducing the heat gas or coolant into the heat exchanger body and for discharging therefrom are not particularly limited. Further, any suitable inlet portion and any suitable outlet portion may be provided to perform the introduction and discharge of the heat gas or coolant. The introducing and discharging of the heat gas or coolant may be performed by a common inlet and outlet portion. Alternatively, the introducing and discharging may be performed by an inlet portion and an outlet portion prepared separately.
Incidentally, the coolant is provided for cooling the hydrogen storage alloy containers and the hydrogen storage alloy heated by the heat gas. The coolant is not limited in kind so long as the provision purpose can be achieved. Generally, air or water is used as the coolant.
A hydrogen-travelling passage is connected to the alloy containers so as to make hydrogen move to the alloy containers. Although the hydrogen-travelling passage can be constituted by a pipe passage or the like, the configuration of the hydrogen-travelling passage according to the present invention is not specifically limited. In short, any material may be used so long as the material can move hydrogen in accordance with storage of hydrogen into alloy containers or release therefrom.
The hydrogen moved through the hydrogen-travelling passage is used in a system using the hydrogen storage and release apparatus according to the present invention. The method of use thereof varies in accordance with the content of the system but is not limited to a specific method of use. For example, hydrogen may be burned as fuel or reserved as purified hydrogen or stored and released by means of another hydrogen storage alloy so as to obtain an air-conditioning, refrigeration output or heat migration.
That is, in the hydrogen storage and release apparatus according to the present invention, heat gas introduced into the heat exchanger body is subjected to heat exchange with the heat exchanging portion on the side relatively low in heat exchanging efficiency, so that the heat of the gas is transmitted to the alloy containers. On the gas introduction side, the heat exchanging efficiency of the heat gas becomes relatively low but the quantity of heat contained by the gas is sufficiently high. Hence, the heat exchange can be performed well and the reduction in the quantity of heat can be suppressed. Hence, the heat gas moves to the discharge side while the quantity of heat carried by the heat gas is kept relatively high. On the other hand, on the discharge side, the heat exchanging efficiency is relatively high, so that heat of the gas is effectively transmitted to the heat exchanging portion, that is, the alloy containers and the hydrogen storage alloy. As a result, the hydrogen storage alloy as a whole is heated evenly regardless of the position of the alloy in the heat exchanger body, so that hydrogen is released evenly from the hydrogen storage alloy.
On the other hand, when the aforementioned setting of the heat exchanging efficiency is not made, heat gas introduced into the heat exchanger body is subjected to heat exchange effectively on the introduction side heat exchanging portion, therefore, a large part of the quantity of heat is lost. In the discharge side heat exchanging portion, the quantity of heat to be transmitted from the gas to the heat exchanging portion is reduced relatively greatly, thus, the heating effect is reduced. As a result, the heating state of the heat exchanging portion, that is, the alloy containers and the hydrogen storage alloy, is made uneven in accordance with the position of the alloy containers and the hydrogen storage alloy in the heat exchanger body. Therefore, release of hydrogen from the discharge side hydrogen storage alloy is delayed greatly. Since a storage and release apparatus performs its function on the basis of release of hydrogen from the hydrogen storage alloys in the apparatus as a whole, a longer time is taken until the discharge side alloy containers which are not effectively heated are to be sufficiently heated. Meanwhile, in this period, the gas introduction-side hydrogen storage alloy is sufficiently heated and continued to be heated even after release of hydrogen from the alloy is achieved. Hence, in the hydrogen storage and release apparatus, hydrogen releasing efficiency depends on the heat exchange state on the discharge side, and total efficiency is lowered. In the present invention, however, uniformity of heat exchange in the heat exchanging portion is attained so that total efficiency is improved.